Optical device, method for cleaning the same, projection aligner, and method of producing the same

ABSTRACT

A reticle (R) is irradiated with an ArF excimer laser beam to transfer a pattern on the reticle (R) onto a wafer (W) through a projection optical system (PL). Each of a plurality of illuminating lens units ( 2 ) arranged in the illuminating optical passage has a barrel containing a plurality of lenses, and caps are so provided as to be spaced from the lenses at both ends. Lens chambers among the lenses are filled with an inert gas, and the spaces between the caps and the lenses are also filled with an inert gas. When the illuminating lens unit ( 2 ) are housed in and illuminating optical path housing, the caps are removed while purging the spaces. Therefore, the lenses at both ends are prevented from being contaminated and the transmittance of the optical lens device for exposure with light having a wavelength of shorter than  300  nm is prevented from lowering.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an exposure apparatus and amethod for manufacturing the same, which has an excimer laser lightsource, a higher harmonics laser light source, a mercury lamp lightsource or the like, each radiating light having an ultraviolet range ofa wavelength of, for example, 300 nm or shorter. The present inventionalso relates to an optical device for a projection optical system or anillumination optical system for use with such an exposure apparatus, andto a method for cleaning such an optical device.

[0002] An exposure apparatus for exposing an image of a pattern of areticle (a photomask or the like) onto a photosensitive substratethrough a projection optical system has been employed in a lithographyprocess for manufacturing semiconductor elements, liquid crystalsubstrates, and so on. Recent years, developments have been performed tomake semiconductor integrated circuits finer and finer, and in order tocomply with such finer integration of semiconductor circuits, there hasbeen attempted to make shorter an exposing wavelength of a light sourcefor use in a lithography process.

[0003] At a current time, an exposure apparatus has already beendeveloped which uses a KrF excimer laser having a wavelength of 248 nmas a light source for a stepper. For example, a higher harmonic wave ofa wavelength variable laser such as Ti-sapphire laser, etc., a quadrupleharmonic wave of a YAG laser having a wavelength of 266 nm, a fivefoldharmonic wave of a YAG laser having a wavelength of 213 nm, a mercurylamp having a wavelength close to 220 nm or a wavelength of 184 nm, andan ArF excimer laser having a wavelength of 193 nm draw attention as acandidate for a light source having a shorter wavelength.

[0004] For conventional exposure apparatuses which use g-rays, i-rays, aKrF excimer laser, or a mercury lamp emitting light rays having awavelength close to 250 nm as a light source, emission spectral rays ofsuch a light source do not overlap with an absorption spectral region ofoxygen, so that they do not cause any decrease in efficiency of lightutilization due to absorption of oxygen and do not suffer from anydisadvantage resulting from the generation of ozone due to theabsorption of oxygen. Therefore, those exposure apparatuses canbasically be used for exposure in ambient atmosphere.

[0005] On the other hand, however, for a light source such as an ArFexcimer laser, emission spectral rays overlap with an absorptionspectral region of oxygen, so that a decrease in efficiency of lightutilization may be caused by the adsorption of oxygen, and thedisadvantage may also result from the generation of ozone due to theabsorption of oxygen. For instance, if it is supposed that atransmittance of an ArF excimer laser light in vacuum or through aninert gas such as nitrogen or helium is 100%/m, the transmittance isdecreased to approximately 90%/m, on the one hand, when the light is ina free-run state, i.e., in a natural emission state, that is, the lightsource is an ArF broad-banded laser, and it is decreased toapproximately 98%/m, on the other hand, even when there is used an ArFlaser with the spectral width narrowed and so narrow-banded as to avoidrays of absorption of oxygen.

[0006] It is considered that the decrease in transmittance is caused dueto the absorption of light by oxygen and an influence of ozonegenerated. The generation of ozone is considered to exert an adverseinfluence upon the transmittance of light (i.e., efficiency of lightutilization) as well as to cause a deterioration in performance ofdevices due to a reaction with a surface of an optical material or otherparts and to cause a pollution of environment.

[0007] For the above-mentioned conventional exposure apparatuses havinga light source such as an ArF excimer laser in the configuration asdescribed above, it is well known that the entire area of a lightpassage is required to be filled with an inert gas such as nitrogen orthe like, in order to avoid a decrease in transmittance of light and ageneration of ozone.

[0008] As a result of various exposure experiments using a projectionexposure apparatus with an excimer laser light source installed thereinand having a relatively large field size, a new phenomenon has now beendiscovered in that the irradiation of an illuminating light in anultraviolet region having a wavelength range of, for example, 350 nm orless (e.g., KrF excimer laser having a wavelength of 248 nm or ArFexcimer laser having a wavelength of 193 nm, etc.) dynamicallyfluctuates transmittance or reflectance of an optical element in aprojection optical system or a coating material (e.g., a thin film for areflection preventive film, or the like) for the optical element in theprojection optical system. It is further found that this new phenomenonfluctuating the transmittance of light dynamically can be caused tooccur in substantially the same way as not only in the case of anoptical element disposed in the projection optical system but also inthe case of an optical element disposed in an illumination opticalsystem for illuminating a reticle. Moreover, likewise, it is also foundthat the such phenomenon is caused to occur in the case of an opticalelement in a light sending system leading the illuminating light leavingfrom a light source disposed under a floor of a clean room to anillumination optical system installed in the main body of the exposureapparatus, and in the case of the reticle (a quartz plate) itself.

[0009] In addition, the such phenomenon is considered to occur, forinstance, due to the attachment of impurities contained in a gas (e.g.,air, nitrogen gas, etc.) present in a space of a projection lightpassage or an illumination light passage, molecules of organicsubstances departing from adhesive or a filling material, etc., for usein fixing optical elements to a barrel, impurities (e.g., watermolecules, hydrocarbon molecules, or other substances diffusing theilluminating light) derived from the inner wall) derived from an innerwall of the barrel (e.g., a coated surface for reflective prevention,etc.), or otherwise, or due to the entry (floating) of such impuritiesor otherwise into the illumination light passage. As a consequence, aserious problem is considered to be caused such that the transmittanceor reflectance of the projection optical system, the illuminationoptical system, and the light sending system fluctuates to a greatextent for a relatively short period of time.

SUMMARY OF THE INVENTION

[0010] The object of the present invention is to provide an opticaldevice which is so arranged as for an optical element including, forexample, lenses constituting a projection optical system, anillumination optical system or a light sending system, or a reflectingmirror or otherwise unlikely to be contaminated, to provide a method forcleaning the optical device, to provide an exposure apparatus using sucha projection optical system, an illumination optical system or a lightsending system, each being unlikely to be contaminated, which has beencleaned by the method for cleaning, and to provide a method formanufacturing the such exposure apparatus.

[0011] Further, the present invention has another object to provide anexposure apparatus that can prevent an optical characteristic (forexample, transmittance or reflectance) of an optical member fromfluctuating by irradiating the optical member with a radiating beamhaving a wavelength of, for example, 350 nm or less.

[0012] Moreover, the present invention has a further object to providean exposure apparatus in which an optical member including, for example,an illumination optical system, a projection optical system or a lightsending system or otherwise, each being incorporated in the exposureapparatus, is so arranged as to be cleaned.

[0013] In order to achieve the object as described above, the opticalapparatus according to the present invention is configured in such amanner that a protective filter is disposed apart in a predetermineddistance between the optical elements, among plural optical elementsdisposed in a barrel, which are disposed on the both end sides in theaxial direction of the barrel, wherein chambers disposed between theplural optical elements and a space between the optical elements on eachof the both end sides and the protective filter is filled with an inertgas in advance.

[0014] The optical device according to the present invention isinstalled in an apparatus for irradiating a mask with an illuminatinglight and exposing a substrate with the illuminating light through themask, wherein an inert gas having the lower capability of absorbing theilluminating light is used as the inert gas to be filled therein. Theilluminating light to be used therefor has a wavelength of 350 nm orless. Further, upon mounting the optical device on a light passagehousing of the illumination optical system installed in the exposureapparatus, it is preferred that the protective filter is detached whilethe space is being purged with the gas and then the housing is filledwith the inert gas, or that the protective filter is detached while thespace is being purged with the gas and a fresh protective filter cleanedin advance is mounted on the both sides in an axial direction of thebarrel, followed by filling the light passage with the inert gas.

[0015] In order to achieve the objet as described above, the presentinvention according to another embodiment provides the optical devicecomprising a gas supply passage for supplying an inert gas to a barrelwith a plurality of optical elements disposed therein; an supply inletconnected to the gas supply passage; a gas discharge outlet fordischarging the inert gas present in the barrel; and a removing memberfor removing a contaminating material, disposed on an inner wall of thegas supply passage.

[0016] The optical device according to the another embodiment of thepresent invention is installed in a device for irradiating a mask withan illuminating light and exposing a substrate with the illuminatinglight through the mask, wherein a gas having a lower capability ofabsorbing the illuminating light is used as the inert gas. As theremoving member, there may be used an adsorbing material or a filter.

[0017] In order to achieve the object as described above, the presentinvention according to a further embodiment provides an optical devicefor use with an exposure apparatus for transferring a pattern on a maskonto a substrate, in which the removing member for removing acontaminating material is mounted on an inner surface of a barrel with aplurality of optical elements disposed therein.

[0018] Further, in order to achieve the object as described above, thepresent invention provides the optical device according to a stillfurther embodiment so adapted as to be used for an exposure apparatusthat transfers a pattern on a mask onto a substrate by irradiating themask with an illuminating light, wherein each of plural chambers formedbetween the plurality of the optical elements disposed in the barrel isprovided with a gas supply inlet and a gas discharge outlet,respectively, for supplying and discharging an inert gas having a lesscapability of absorbing the illuminating light, and each of the gassupply inlet and the gas discharge outlet is provided with anopening-closing valve for opening and closing the gas supply inlet andthe gas discharge outlet, respectively.

[0019] In addition, in order to achieve the object as described above,the present invention in another aspect provides a light cleaning methodfor cleaning the optical device for use with an exposure apparatus fortransferring a pattern on a mask onto a substrate by irradiating themask with an illuminating light, the optical device being configured insuch a way that each of chambers formed between a plurality of opticalelements disposed in a barrel is provided with a gas supply inlet and agas discharge outlet for supplying and discharging a gas having a lessercapability of absorbing the illuminating light, respectively, and thatthe gas supply inlet and the gas discharge outlet are each provided withan opening-closing valve for opening and closing the gas supply inletand the gas discharge outlet, respectively; wherein the optical deviceis cleaned by the light cleaning method comprising the step for fillingthe barrel with the gas to a predetermined pressure in such a state thatthe opening-closing valve of the gas supply inlet is opened while theopening-closing valve of the gas discharge outlet is closed; the stepfor allowing a contaminating material attached on a surface of theoptical elements to float by irradiating the optical elements with theilluminating light in such a state that the opening-closing valves ofthe gas supply inlet and the gas discharge outlet are both closed; thestep for flowing the gas outside and inside the barrel by opening theopening-closing valve of the gas supply inlet and the opening-closingvalve of the gas discharge outlet; and the step for closing theopening-closing valves of the gas supply inlet and the gas dischargeoutlet, respectively.

[0020] With the above configuration, it is also possible to flow theinert gas through each of the plural chambers in such a state that theopening-closing valves of the gas supply inlet and the gas dischargeoutlet are both opened, prior to closing the opening-closing valve ofthe gas discharge outlet. Moreover, the optical device may be configuredin such a manner that the plural chambers are divided into at least twogroups, each group having a predetermined number of chambers, and eachgroup is provided with a gas supply inlet and a gas discharge outlet aswell as the gas supply inlet and the gas discharge outlet are eachprovided with an opening-closing valve.

[0021] Furthermore, in order to achieve the object as described above,the present invention provides a projection exposure apparatus fortransferring a pattern on a mask onto a substrate through a projectionoptical system by irradiating the mask with an illuminating light,wherein a plurality of chambers, each chamber being formed between aplurality of optical elements disposed in a barrel and provided with agas supply inlet and a gas discharge outlet for supplying anddischarging an inert gas having a lesser capability of absorbing theilluminating light, respectively, and the gas supply inlet and the gasdischarge outlet being each provided with an opening-closing valve;wherein the optical device is so arranged as to be cleaned by a lightcleaning method comprising the step for filling the barrel with the gasto a predetermined level of pressure in such a state that theopening-closing valve of the gas supply inlet is opened while theopening-closing valve of the gas discharge outlet is closed; the stepfor allowing a contaminating material attached on a surface of theoptical elements to float by irradiating the optical elements with theilluminating light in such a state that the opening-closing valves ofthe gas supply inlet and the gas discharge outlet are both closed; thestep for flowing the gas outside and inside the barrel by opening theopening-closing valve of the gas supply inlet and the opening-closingvalve of the gas discharge outlet; and the step for closing theopening-closing valves of the gas supply inlet and the gas dischargeoutlet, respectively.

[0022] The optical device according to the present invention may also beused as the projection optical system and/or the illumination opticalsystem for irradiating the mask with the illuminating light.

[0023] In order to achieve the object as described above, the presentinvention in a further aspect provides an exposure apparatus fortransferring a pattern on a mask onto a substrate, which comprises anoptical system interposed between a light source for emitting anilluminating beam and the substrate; a protective filter disposed atleast at an end of a barrel for holding an optical element; and anoptical unit having a gas having a lesser capability of absorbing theilluminating beam filled in the barrel, the optical unit being disposedin the optical system.

[0024] With the above configuration, the optical device according to thepresent invention contains an illumination optical system forirradiating the mask with the illuminating beam and has the optical unitdisposed in the illumination optical system. Upon mounting the opticalunit on the optical system, the protective filter may be detached fromthe barrel or a new protective filter is exchanged for the older one.Preferably, the optical device according to the present invention isfurther provided with a gas supply device for supplying an inert gashaving a lesser capability of absorbing the illuminating beam, which isdisposed in the optical system, and the gas supply device is to beoperated after the illuminating beam has been emitted in such a statethat the optical system is filled with the inert gas. Moreover, it ispreferred that the optical device is further provided with a gas exhaustdevice for discharging the inert gas present in the optical system andthat the gas exhaust device is operated prior to filling or supplyingthe optical system with the inert gas. The illuminating beam to be usedtherefor may have a wavelength preferably in the range of from 100 nm to200 nm, and it may preferably include, for example, ArF laser or F₂laser. Moreover, the inert gas may preferably include, for example,nitrogen, helium, or the like.

[0025] In addition, in order to achieve the object as described above,the present invention in a still further embodiment provides theexposure apparatus for transferring a pattern on a mask onto asubstrate, which comprises an optical system interposed between a lightsource for emitting an illuminating beam and the substrate; a gas supplydevice for supplying an inert gas having a lesser capability ofabsorbing the illuminating beam to at least a portion of the opticalsystem; and a gas exhaust device for discharging the inert gas from theportion of the optical system prior to the supply of the inert gas.

[0026] With the above configuration, the optical device according to thepresent invention may contain an illumination optical system forirradiating the mask with the illuminating beam, a light sending systeminterposed between the light source and the illumination optical system,and a projection optical system for projecting the illuminating beamleaving from the mask onto the substrate. With this configuration, it ispreferred that the gas exhaust device and the gas supply device areoperated one after another in this order after the optical system hasbeen cleaned by means of light by irradiating the optical system withthe illuminating beam. The illuminating beam to be used therefor mayhave a wavelength preferably in the range of from 100 nm to 200 nm, andit may preferably include, for example, ArF laser or F₂ laser. Moreover,the inert gas may preferably include, for example, nitrogen, helium, orthe like.

[0027] In order to achieve the object as described above, the presentinvention in a still further aspect provides a method for the productionof the exposure apparatus, which comprises locating a protective filterat least at an end of a barrel holding optical elements, filling thebarrel with an inert gas having a lesser capability of absorbing theilluminating beam, and locating the barrel between a light source foremitting the illuminating light and the substrate.

[0028] In the method for the production of the exposure apparatusaccording to the present invention, the protective filter is detached ora new protective filter is exchanged for the older protective filter,after the barrel has been disposed.

[0029] Moreover, in order to achieve the object as described above, thepresent invention in a still further embodiment provides a method forthe production of the exposure apparatus for exposing the substrate tothe illuminating beam through the mask, which comprises irradiating atleast a portion of the optical system capable of allowing theilluminating beam to pass therethrough with a cleaning light forcleaning the optical system and replacing the gas present in the opticalsystem with a gas having a lesser capability of absorbing theilluminating beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a schematic illustration of an exposure apparatus in anembodiment of the present invention.

[0031]FIG. 2 is a view showing details of a gas cell GS.

[0032]FIG. 3 is a schematic illustration showing an illuminating lensunit 2; in which

[0033]FIG. 3(a) is a sectional view; and

[0034]FIG. 3(b) is an enlarged view showing a portion of a quick couplerQ1 of FIG. 2(a).

[0035]FIG. 4 is a view for explaining procedures of mounting theilluminating lens unit 2 on an illumination optical system IL.

[0036]FIG. 5 is a sectional view showing a projecting lens unit 4.

[0037]FIG. 6 is a view showing a first variation of the projecting lensunit of FIG. 5.

[0038]FIG. 7 is a view showing a second variation of the projecting lensunit of FIG. 5.

[0039]FIG. 8 is a sectional view showing a tubular path L12 as shown inFIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

[0040] A description will be made of the embodiment according to thepresent invention with reference to FIGS. 1 to 8.

[0041]FIG. 1 is a view for schematically explaining an exposureapparatus according to the embodiment of the present invention. As shownin FIG. 1, a light source 1 for emitting an ArF excimer laser light isdisposed separately from a chamber in which the main body of theexposure apparatus is housed. A portion of the light beam leaving fromthe light source 1 is transmitted through a light sending system, thatis, a beam splitter (a partial mirror) Mp to a mirror M_(I1) while theremaining is reflected and then travels toward a mirror M. The lightpassed through the beam splitter Mp is reflected at mirrors M_(I1) andM_(I2) in the light sending system and at a mirror M_(I3) in anillumination optical system IL, thereby illuminating a reticle R in auniform manner through an illuminating lens unit 2 disposed in theillumination optical system IL. FIG. 1 shows an integral combination ofthe light sending system and the illumination optical system IL. In FIG.1, only one illuminating lens unit 2 is shown, although in usual casesthe illumination optical system IL comprises a plurality of illuminatinglens units 2 (containing, e.g., a flyeye lens unit, a relay lens unit, acondenser lens unit, etc.). The light sending system and theillumination optical system IL are enclosed with a container, and thecontainer is supplied with a gas having no or a lesser capability ofabsorbing an ArF light, such as, for example, nitrogen gas (or heliumgas), through a valve V1. Although not shown, the reticle R is loaded ona stage and allowed to be transferred relatively to the illuminatinglight leaving through a slit or otherwise of a vision field stop of theillumination optical system IL.

[0042] The light passed through the reticle R is transmitted through avariety of optical members constituting an projection optical system PL,e.g., a lens element and/or a mirror, onto the surface of a wafer Wloaded on a wafer stage WS, and a pattern formed on the reticle R isimaged on the surface of the wafer W. The wafer stage WS is so arrangedas to transfer the wafer W in a direction relative to the light leavingfrom the reticle R by irradiating it with the illuminating light andpassing through the projection optical system PL. Upon exposure, thereticle R and the wafer W are scanned in directions opposite to eachother at a velocity ratio corresponding to a magnification of theprojection optical system. The projection optical system PL is providedwith at least one projecting lens unit 4, and the projection opticalsystem PL is enclosed with a container in substantially the same manneras the illumination optical system IL. The container is supplied with anitrogen gas or otherwise through a valve V2. The details of theilluminating lens unit 2 and the projecting lens unit 4 will bedescribed hereinafter.

[0043] The container for enclosure of the illumination optical system ILis provided with a valve V3 for discharging nitrogen gas therefrom, andthe nitrogen gas discharged from the valve V3 is sent to an exhaust ductby the aid of a rotary pump RP. The container is also provided with avalve V4 for discharging nitrogen gas therefrom, and the nitrogen gasdischarged through the valve V4 is then supplied to an exhaust ductthrough the rotary pump RP. The light left from the light source 1 andreflected at the beam splitter Mp is then reflected by means of aplurality of mirrors M disposed and arranged in an appropriate manner,and enters into a gas cell GS through a lens L. The gas cell GS issupplied with nitrogen gas through a pressure reducing valve RG. Asshown in FIG. 2, the gas cell GS is provided with an orifice O, and thelens L is disposed so as to seal the orifice O. The light entering intothe gas cell GS through the lens L is so arranged as to be focused on anaxis connecting a gas supply inlet 10 to a gas discharge outlet 11. Thenitrogen gas is ionized in the gas cell GS by the two-photon absorptionaction of ultraviolet light.

[0044] The ionized nitrogen gas discharged from the gas cell GS isdivided into three paths, each being supplied to a container enclosingthe reticle R and a reticle stage through a valve V5, to a bottom endportion of the projection optical system PL through a valve V6, and tothe wafer WS through a valve V7. The container for enclosing the reticleR and the reticle stage is provided with a valve V8 through which thenitrogen gas is discharged. The nitrogen gas discharged through thevalve V8 is supplied to an exhaust duct through an oxygen sensor S andthe rotary pump RP.

Detailed Description of Illuminating Lens Unit

[0045]FIG. 3(a) is a view in section of the illuminating lens unit 2disposed in the illumination optical system IL. A barrel 26 has lenses21 to 25, inclusive, and lens separation rings 27 to 30, inclusive,disposed each so as to hold the lenses in a predetermined distance fromone another. Moreover, the lenses and the lens separation rings arefixed to the barrel 26 by means of a pressing ring 31. The barrel 26 ishoused in a casing 32, and caps 33 and 34 are mounted on the top andbottom openings (when looked at the drawing) of the casing 32 throughO-ring seals S1 and S2, respectively. The cap 33 is configured such thata glass member 36 is mounted on a frame 35, and the cap 34 is configuredsuch that a glass member 38 is mounted on a frame 37. The casing 32 isprovided with a tubular path L3 a for supplying nitrogen gas and atubular path L3 b for discharging the nitrogen gas, and the tubularpaths L3 a and L3 b are provided with valves V10 and V11, respectively.The tubular path L3 a for the supply of the gas is divided into threetubular path divisions L3 a ₁, L3 a ₂ and L3 a ₃, the tubular pathdivision L3 a ₁ being connected to a gas supply inlet G1 through a quickcoupler Q1, the tubular path division L3 a ₂ being connected to a gassupply inlet G2 through a quick coupler Q2, and the tubular pathdivision L3 a ₃ being connected to a gas supply inlet G1 through a quickcoupler Q3. On the other hand, the tubular path L3 b is connected to agas discharge outlet G4 through a quick coupler Q4.

[0046]FIG. 3(b) is an enlarged view of the portion of the quick couplerQ1 of the tubular path division L3 a ₁. As shown in FIG. 3(b), achemical filter F is disposed on the downstream side of the quickcoupler Q1 so as to prevent a contaminating material from entry into thecasing 32. Likewise, the other tubular path divisions L3 a ₂ and L3 a ₃are provided each with a chemical filter F. A description will be madeof the chemical filter F hereinafter.

[0047] As the nitrogen gas has been supplied from the tubular path L3 a,the nitrogen gas supplied to the gas supply inlet G1 through the tubularpath division L3 a ₁ is flown through a lens chamber interposed betweenthe cap 33 and the lens 21 in the direction as indicated by the arrowA1, and the nitrogen gas is then discharged through the gas dischargeoutlet G4 into the tubular path L3 b. On the other hand, the nitrogengas supplied to the gas supply inlet G2 through the tubular pathdivision L3 a ₂ is allowed to flow through a lens chamber interposedbetween the lenses 21 and 22 and then through a lens chamber interposedbetween the lenses 22 and 23 in the direction as indicated by the arrowA2, followed by passing through a lens chamber interposed between thelenses 23 and 24 in the direction as indicated by the arrow A3, andthrough a lens chamber interposed between the lenses 24 and 25 in thedirection as indicated by the arrow A4, then followed by discharging thenitrogen gas through the gas discharge outlet G4 to the tubular pathdivision L3 b. Further, the nitrogen gas supplied to the gas supplyinlet G3 through the tubular path L3 a ₃ is allowed to pass through alens chamber interposed between the cap 34 and the lens 25 in thedirection as indicated by the arrow A5 and then discharged through thegas discharge outlet G4 to the tubular path L3 b.

[0048] The barrel 26 is assembled in ambient atmosphere in usual cases,so that attachment of a contaminating material to the surfaces of thelenses 21 to 25 is inevitable. In accordance with the present invention,however, the illuminating lens unit 2 is configured such that thecontaminating material attached to each of the lenses 21 to 25 can beremoved easily and readily in a way as will be described hereinafter andfurther that attachment of such a contaminating material to the surfaceof a lens can be avoided upon assembly of the illuminating lens unit 2with the illumination optical system IL.

[0049] More specifically, first, the casing 32 is exhausted in a vacuumstate by opening the valve V11 in such a state that the valve V10 isclosed. Thereafter, the valve V11 is closed and the valve V10 is openedto supply the casing 32 with nitrogen gas and fill the casing 32 withthe nitrogen gas. In this state, each of the lenses 21 to 25, inclusive,is irradiated with ArF light through a glass member of the cap 33. Asthe lenses are irradiated with the ArF light, then the contaminatingmaterial attached on the surface of each of the lenses 21 to 25 and aninner surface of each of glass members 36 and 38 is allowed to beremoved therefrom and to float in the nitrogen gas. While the lenses areirradiated in the manner as described above, the valve V11 is opened andthe nitrogen gas present in the casing 32 is allowed to be discharged,thereby resulting in discharging the contaminating material floating inthe nitrogen gas outside the casing 32. Then, the valve V11 is closed inthe state in which the casing 32 is supplied with the nitrogen gas, andthe pressure in the casing 32 is adjusted so as to reach a predeterminedlevel. As the pressure has reached the predetermined level, then thevalve V10 is closed, and the illuminating lens unit 2 is stored in thisstate. Alternatively, unlike in the above-mentioned state in which thecasing 32 is filled with the nitrogen gas, the contaminating materialmay also be removed by irradiating the illuminating lens unit 2 with ArFlight or light beams having wavelengths of 185 nm and 254 nm, emittingfrom a low-pressure mercury lamp, while keeping the nitrogen gasflowing. In the latter case where the low-pressure mercury lamp is used,the low-pressure mercury lamp is arranged in a row with the light source1 and the light beam emitting from the low-pressure mercury lamp is ledto the light sending system by means of a lens and/or a mirror. In thiscase, however, the optical system disposed behind the low-pressuremercury lamp and the light source may also be used in substantially thesame manner as described above.

[0050] With the configuration as described above, the contaminatingmaterial attached to the surfaces of the lenses 21 to 25 can be removedeasily and readily upon assembly of the barrel 26. Moreover, this mannercan avoid the contamination of the lenses 21 to 25 until theilluminating lens unit 2 is assembled with the illumination opticalsystem IL.

[0051] Then, a description will be made of the procedures of theassembly of the illuminating lens unit 2 with the illumination opticalsystem IL with reference to FIG. 4. First, the illumination opticalsystem IL is wide open to ambient atmosphere, and the tubular path L3 aof the illuminating lens unit 2 is connected to a nitrogen gas supplyline of the valve V1 disposed in the illumination optical system IL.Then, the valves V1 and V10 are opened and the valve V11 is closed tosupply the casing 32 with the nitrogen gas. Further, after the caps 33and 34 (see FIG. 3) are detached while the nitrogen gas has beensupplied, the valve V11 is opened and the illumination optical system ILis closed. At this time, the nitrogen gas is allowed to flow in each ofthe lens chambers in the direction as indicated by the respective arrowsAl to A4, inclusive, and the nitrogen gas to be supplied through thetubular paths L3 a and L3 b is allowed to flow in the direction asindicated by the arrow A6, so that the surface on the opening side ofeach of the lenses 21 and 25 is blocked from the open atmosphere by thenitrogen gas. In this configuration, the contamination of the lenses 21to 25 can be prevented even upon assembly of the illuminating lens unit2 with the illumination optical system IL.

[0052] As will be described hereinafter, the illumination optical systemIL is exhausted in a vacuum state through the valve V3 after theassembly of the illuminating lens unit 2 with the illumination opticalsystem IL, and the nitrogen gas is supplied to the illuminating lensunit 2 through the valve V1. At this time, the nitrogen gas supplied tothe tubular path L3 a through the quick coupler Q5 is allowed to flowinto the illumination optical system IL after circulation through theilluminating lens unit 2 and discharged toward the outside through thevalve V3. Although the caps 33 and 34 have been detached upon assemblyof the illuminating lens unit 2 with the exposure apparatus in themanner as described above, the such assembly can also be made in somedevice configuration without detaching the caps 33 and 34. In such acase, as the surface on the atmospheric side of each of the glassmembers 36 and 38 of the respective caps 33 and 34 is contaminated withwater or otherwise, the contaminating material can be removed thoroughlyfrom the illuminating lens unit 2, for instance, simply by exchangingnew caps non-contaminated for the old caps 33 and 34. It is further tobe noted herein that the method for removing the contaminating materialby supplying the nitrogen gas and irradiating the illuminating lens unit2 with the illuminating light in the manner as described above can alsobe applied to the projecting lens unit 4, without limiting to theilluminating lens unit 2.

Description of the Details of the Projecting Lens Unit 4

[0053]FIG. 5 is a view in section of an outline of the projecting lensunit 4 to be disposed in the projection optical system PL. A barrel 41of the projecting lens unit 4 has three lenses 42, 43 and 44 disposed ina relationship spaced apart in a predetermined distance from oneanother, and fixed thereto by means of a pressing ring 45. Referencenumeral 46 denotes a lens separation ring for holding the lenses 43 and44 apart in a predetermined distance from each other. It should be notedherein, however, that although the projecting lens unit 4 is providedwith a number of lenses in an actual case, FIG. 5 shows only threelenses for brevity of explanation. A lens chamber R1 is formed betweenthe lenses 42 and 43, and a lens chamber R2 is formed between the lenses43 and 44. The lens chamber R1 is provided with a gas supply inlet G6having a quick coupler Q6 mounted thereon and with a gas dischargeoutlet G7 having a quick coupler Q7 mounted thereon. On the other hand,the lens chamber R2 is provided with a gas supply inlet G8 having aquick coupler Q8 mounted thereon and with a gas discharge outlet G9having a quick coupler Q9 mounted thereon. Between the gas supply inletG6 and the quick coupler Q6 is interposed a chemical filter F1.Likewise, between the gas supply inlet G8 and the quick coupler Q8 isinterposed a chemical filter F2. The chemical filters F1 and F2 aredisposed with the attempt to remove impurities such as, for example,organic substances and alcohols, present in the nitrogen gas to besupplied.

[0054] Now, a description will be made of details of the chemicalfilter. As a filter for removing ions, there may be used, for example,an ion exchange resin, an ion exchange fiber, or the like. As a filterfor use in treating gases, an ion exchange fiber is preferred in termsof a larger surface area, a higher reaction velocity, and easiness ofprocessing. Such an ion exchange fiber may be prepared by graftpolymerization of a polymer fiber such as, for example, polypropylenefiber, by means of radiation. The ion exchange fiber may be divided intotwo groups, i.e., an acidic cation exchange fiber and a basic anionexchange fiber. An acidic cation exchange fiber may be preferably usedfor an positive ion such as, for example, NH₄ ⁺ or an amine ion, or abasic gas, and a basic anion exchange fiber may be preferably used for anegative ion such as, for example, SO₄ ²⁻ or NOx, or an acidic gas.

[0055]FIG. 5 shows the quick couplers Q6 to Q9 having valves V16 to V19mounted on tubular paths L16 to L19 thereof, respectively, in order tocontrol a flow of the gas to be supplied through each of the gas supplyinlets G6 and G8 for each of the lens chambers R1 and R2, respectively.In the case of the projecting lens unit 4, too, it is inevitable that acontaminating material is attached to surfaces of the lenses 42 to 44,inclusive, upon assembly of a barrel thereof, likewise in the case ofthe illuminating lens unit 2 in the manner as described above. In thiscase, too, such a contaminating material attached to the surfaces of thelenses for the projecting lens unit 4 can also be removed insubstantially the same procedures as in the case of the illuminatinglens unit 2, i.e., by irradiating the projecting lens unit 4 with ArFlight while flowing nitrogen gas through the gas supply inlets G6 andG8. A description of the specific procedures for removing such acontaminating material from the projecting lens unit 4 will be omittedfrom the following explanation because they are substantially the sameas in the case of the illuminating lens unit 2.

[0056] In the embodiment as shown in FIG. 5, the tubular paths L16 andL19, inclusive, are provided each with a valve so as to control a flowof a gas for each of the lens chambers R1 and R2. It should be notedherein, however, that, as long as a flow amount of a gas that flowsthrough the lens chambers R1 and R2 is not reduced to an extremely lowextent, tubular paths L16 and L18 are combined into one tubular pathL12, on the one hand, and tubular paths L17 and L19 are combined intoone tubular path L13, on the one hand, and the combined tubular pathsL12 and L13 are provided with valves V12 and V13, respectively, as shownin FIG. 6, in order to control a flow of the gas through the projectinglens unit 4. Although FIG. 6 shows only three lenses for the projectinglens unit 4 and only one lens chamber for collectively discharging thegas therefrom, the projecting lens unit 4 is actually provided with anumber of lenses so that a plurality of lens chambers are formed.Therefore, in such a case, the number of the lens chambers forcollectively discharging the gas for a plurality of lenses may be two ormore. A gas supply inlet and a gas discharge outlet are provided foreach of the lens chambers as shown in FIGS. 5 and 6, however, a line maybe provided only for a lens chamber that can be expected to achieve thehighest effect from the design point of view.

[0057]FIG. 7 shows a variation of the projecting lens unit as shown inFIG. 6, in which the portions and elements identical to those as shownin FIG. 6 are provided with the identical reference numerals andsymbols. A description will be made mainly of the portions and elementsthat differ from those of FIG. 6. As shown in FIG. 7, a projecting lensunit 4′ has an inner wall surface of each of the lens chambers R1 and R2as well as an inner wall surface of the tubular path L12 for supply of agas coated with an adsorbing material Ad in order to remove water and soon present in a nitrogen gas to be supplied through a nitrogen gassupply source T. The adsorbing material may include, for example,activated carbon, silica gel, zeolite, and so on. In FIG. 7, referencesymbol LF sets forth a line filter, and reference symbol V14 sets fortha valve.

[0058] Then, a description will be made of the operation of theilluminating lens unit 2 and the projecting lens unit 4, each having theconfiguration as described above, after they are assembled with theexposure apparatus. Each of the illumination optical system IL, theprojection optical system PL and the reticle R is enclosed with acontainer from which in turn the air is exhausted into a vacuum statesequentially by the action of the rotary pump RP through the valves V3,V4 and V8, respectively. At this time, the air is discharged from theinside of each of the illuminating lens unit 2 and the projecting lensunit 4 to a vacuum state in the like manner. The degree of vacuum ineach of the containers can be known on the basis of the concentration ofoxygen to be detected by an oxygen sensor S mounted on each of therespective containers. After the vacuum state has been realized to apredetermined level, the container enclosing each of the illuminationoptical system IL and the projection optical system PL is supplied withnitrogen gas to a level higher than the atmospheric pressure through thevalves V1 and V2, respectively. Further, the container enclosing thereticle R is supplied with an appropriately ionized nitrogen gas toamount to a level higher than the atmospheric pressure through the valveV5. The ionized nitrogen gas can remove static electricity caused to begenerated in the reticle R, thereby preventing an occurrence of damagesof the reticle R resulting from static electricity.

[0059] On the other hand, an ionized nitrogen gas is supplied toward thewafer W in a space between the projection optical system PL and thewafer W through the valve V6 in the direction nearly perpendicular tothe wafer W. In addition, an ionized nitrogen gas is further suppliedthrough the valve V7 so as to block the surface of the wafer W from theopen atmosphere. This can remove static electricity generated on thesurface of the wafer W by means of the action of the ionized nitrogengas supplied, thereby preventing the wafer W from being damaged orstained by static electricity.

[0060] Upon subjecting the wafer W to projection exposure or exchangingwafers, an ionized nitrogen gas is supplied in a generally continualmanner to a space between the projection optical system PL and the waferW. Therefore, the nitrogen gas atmosphere will not be broken in asubstantial manner even upon exchanging wafers. Moreover, only when thereticle R has to be exchanged, it is required that an ionized nitrogengas has to be supplied to a container enclosing the reticle R by drawinga vacuum after exchanging reticles. On the other hand, for a containerenclosing the illumination optical system IL and the projection opticalsystem PL, the valves V1 to V4, inclusive, may be closed in a state inwhich it is filled with an ionized nitrogen gas or an ionized nitrogengas may be supplied in a continual manner. In particular, the continualsupply of the ionized nitrogen gas presents the advantages as will bedescribed hereinafter.

[0061] Even if contaminating materials would have been removed after theassembly of the illuminating lens unit 2 and the projecting lens unit 4in the manner as described above, there is the risk that the surfaces oflenses may be contaminated with moisture and so on after the assemblywith the exposure apparatus by causing moisture and so on attached tothe inner wall surfaces of the casing 32 and the lens chambers R1 and R2to be released. However, when the ionized nitrogen gas is suppliedcontinually after the assembly in the manner as described above, each ofthe lenses is irradiated with ArF light by the exposure operation andthe irradiation of such ArF light allows the contaminating materialsreleased from the lens surfaces to be exhausted outside the containertogether with the nitrogen gas. Therefore, the lens surfaces are notcontaminated again with moisture and so on even if they would bereleased from the inner surfaces thereof. In the embodiment as describedabove, a description has been made by taking the illuminating lens unit2 and the projecting lens unit 4, each consisting of plural lenses, asan example, however, it should be noted herein that the presentinvention can be applied in a like manner to an optical systemconsisting of reflecting mirrors.

[0062] When such an inert gas has been flown continually inside andoutside the barrel in the manner as described above, adhesive or fillingmaterial used for fixing an optical element such as, for example, alens, or the like to the barrel (a holding member) of the illuminationoptical system, the projection optical system or the light sendingsystem in the exposure apparatus is irradiated with radiating beamshaving an ultraviolet wavelength region and gases consisting of organicmaterials, etc. derived from the adhesive or filling material, orreaction products, etc. resulting from such gases may be generated. Evenin such a case, this can prevent such gases from attaching to theoptical member or entering into the optical path and floating therein.This can also prevent a fluctuation in optical characteristics (e.g.,transmittance, reflectance, etc.) of optical members, which may becaused by the irradiation with light beams, or in opticalcharacteristics such as, for example, focal distance, projectionmagnification, five aberrations of Seidel, telecentricity, etc. in theprojection optical system. As a consequence, a fluctuation in theintensity of illuminating light on the mask or substrate can beprevented, so that a pattern of a mask can be transferred onto asubstrate always at an appropriate amount of exposing light, and animage of the pattern on the mask can be projected on the substratealways under appropriate imaging conditions.

[0063] In addition, the present invention can be applied to the readyimplementation of a so-called light cleaning operation for opticalmembers in an exposure apparatus for use in the lithography process formanufacturing micro devices such as semiconductor elements, thin layermagnetic heads, image pickup elements (CCD) and so on, by utilizing themethod for the removal of contaminating materials in the manner asdescribed above. The present invention allows contaminating materialsattached on the surface of the optical member (e.g., gases derivedtherefrom or reaction products resulting from such gases, or impuritiessuch as, for example, water or hydrocarbons to be generated from theinner wall of the barrel, etc.) to be removed simply by irradiating theoptical member of the illumination optical system, the projectionoptical system or the light sending system or otherwise with light beamsor illuminating light for exposing, for example, having a wavelength of185 nm or 254 nm, while the illumination optical system, the projectionoptical system or the light sending system or otherwise is incorporatedinto the exposure apparatus.

[0064] The optical system to be installed in the exposure apparatus towhich the optical device or the cleaning method according to the presentinvention can be applied may include, for example, an illuminationoptical system consisting of a plurality of optical elements such as,for example, optical integrators (flyeye lenses) or condenser lenses andilluminating a mask with an exposing light, or a projection opticalsystem (including, for example, a catadioptric optical system)consisting of a plurality of optical elements (refracting elementsand/or reflecting elements) arranged along the optical axis thereof andprojecting an image of a pattern formed on a mask onto a substrate (suchas, for example, a semiconductor wafer, etc.). Moreover, they mayinclude optical systems which comprise, for example, (1) a light sendingsystem having at least one optical element (such as, for example, amovable mirror, parallel flat panel, etc.) for adjusting the positionrelationship of the optical axis of the illumination optical system withthe illuminating light and leading the illuminating light leaving from alight source disposed on a floor of a clean room separately from themain body of the exposure apparatus; (2) an alignment optical system fordetecting the position of an alignment mark on the mask or the substrateby irradiating the mask or the substrate with the illuminating lighthaving an ultraviolet wavelength region; and (3) an optical system of ameasurement device for detecting optical characteristics (such as, forexample, projection magnification, etc. as described above) of theprojection optical system, which is so configured such that a lightgenerating from a mark and passing through the projection optical systemis received when a reference mark or a measurement mark on a stage withthe mask or the substrate loaded thereon is irradiated with an exposinglight or an illuminating light having the wavelength substantially equalto that of the exposing light.

[0065] Moreover, when the present invention is applied to the alignmentoptical system as described above, a fluctuation in the intensity of theilluminating light (an alignment light) to be irradiated on thealignment mark, which may be caused by a fluctuation in thetransmittance or reflectance of the optical member, can be prevented.Further, a deterioration in the telecentricity of the illuminating lightand so on can also be prevented, which may be caused by a decrease inuniformity of illuminance of the illuminating light on the alignmentmark, i.e., by the formation of an irregularity in illuminance, due tothe presence of such gases derived from the adhesive or fillingmaterials used for fixing the optical members to the barrel or suchreaction products from such gases, or by a decrease in uniformity of thelight intensity in a pupil region of the alignment optical systemthrough which a light flux of the illuminating light focusing on onepoint on the alignment mark passes. As a consequence, the mask can bealigned with the substrate at a high degree of precision without causingany decrease in precision of detecting the position of the alignmentmark.

[0066] In addition, when the present invention is applied to themeasurement optical system, like the alignment optical system, there canbe prevented a fluctuation in the intensity of the illuminating light onthe mark due to a fluctuation in the transmittance or reflectance of theoptical member, as well as an irregularity of illuminance and a decreasein telecentricity. As a result, the optical characteristics of theprojection optical system can be detected at a high degree of precision.

[0067] It can also be noted herein that the present invention canfurther be applied to an exposure apparatus which uses F₂ laser having awavelength of 157 nm as an exposing light source. In other words, thepresent invention is effective for a vacuum ultraviolet light (VUVlight) having a wavelength region of 100 nm to 200 nm, particularly fora VUV light having a wavelength region of 150 nm to 200 nm. This isbecause a light having a wavelength region shorter than 150 nm may belikely to undergo the limitations to a large extent from a glassmaterial, a coating material, and so on.

[0068] It can now be noted herein that the terms as referred to in theembodiments as described above correspond to the elements as used in theclaims section of the specification of this application as will bereferred to herein. In the embodiments of the present invention asdescribed above, the reticle R corresponds to a mask as referred to soin the claims section of the specification; the illuminating lens unit 2and projecting lens units 4 and 4′ to an optical lens device; caps 33and 34 each to a protective filter; tubular path L12 to a supplypassage; and the valve V12 to a movable member. It is further to benoted herein that the term “inert gas” referred to in this specificationshould be understood to include nitrogen gas.

[0069] As described above, the present invention can offer the effectsas will be described hereinafter.

[0070] As the protective filer defining a predetermined space isprovided between both ends of each of the plural optical elements, andnot only each of the spaces between the optical element and theprotective filter but also each of the chambers disposed between theplural optical elements are filled with an inert gas, each of thechambers and the spaces can be purged and cleaned with the inert gasafter the assembly of a single body of the optical device, therebyassembling the optical device with the projection exposure apparatus ina state in which the optical elements located on the both sides are notcontaminated.

[0071] Further, as the optical device is assembled while the spaceinterposed between the protective filter and the optical elementsdisposed on the both sides thereof is purged with such an inert gas, theoptical elements or the protective filter can be prevented fromcontamination at the time of assembly.

[0072] Moreover, in accordance with the present invention, theprotective filter is detached while the space interposed between theprotective filter and the optical elements on the both sides thereof anda pre-cleaned protective filter is then mounted thereon, so that theoptical elements or the protective filter can be prevented fromcontamination at the time of assembly.

[0073] An adsorbing material is mounted on an inner face of the supplypassage of the inert gas and the barrel, so that a contaminatingmaterial in the inert gas supplied, if it is present therein, can beadsorbed on the absorbing material, and there can be avoided the riskthat the surface of the lens or the reflecting mirror is contaminated.

[0074] In addition, a filter is disposed on the side downstream of themovable member such as an electromagnetic valve, so that a contaminationof the surface of the lens and the surface of the reflecting mirror withthe contaminating material generating from the movable member can beprevented.

[0075] Furthermore, the contaminating materials can be removed for surebecause each of the chambers among the plural optical elements is soarranged that it can be purged individually with the inert gas.

[0076] Moreover, the plural chambers interposed each between the pluraloptical elements are divided into at least two groups, each groupcontaining a predetermined number of chambers, and each group can bearranged so as to be purged with an inert gas. Therefore, a number ofvalves for controlling the passage of a gas can be minimized, so thatthis construction can contribute to a reduction in costs formanufacturing the optical device as a whole.

[0077] Also, the contaminating materials attached to the opticalelements can be caused to be afloat by the irradiation with theilluminating light after the optical device has been filled with theinert gas, and then the inert gas, together with the floatingcontaminating materials, can be discharged from the optical device.Therefore, the contaminating materials attached to the surface of eachoptical element can be removed in such a state that the optical deviceis assembled as a single body.

[0078] In accordance with the present invention, a precleaned opticaldevice can be assembled with the projection exposure apparatus as anillumination optical system or a projection optical system, so that adecrease in transmittance for the lenses or in reflectance for areflecting mirror can be controlled even immediately after assembly.

[0079] Further, the present invention can prevent the optical systemsuch as the projection optical system, the light sending system, and soon from being contaminated, so that a fluctuation in the opticalcharacteristics of the optical system such as the projection opticalsystem, the light sending system, and so on can be controlled, andprojection exposure at a high degree of precision can be implemented.

What is claimed is:
 1. An optical device comprising: a protective filterinterposed at each of both ends of a barrel with plural optical elementsdisposed therein; wherein the plural optical elements are locatedbetween the protective filters; and; wherein an inert gas is filled inadvance in a chamber between the plural optical elements and a spacebetween the optical elements on both end sides thereof and theprotective filter.
 2. The optical device as claimed in claim 1 ,wherein: the optical device is installed in an apparatus to irradiate amask with an illuminating light and to expose a substrate to theilluminating light through the mask; and the inert gas is an inert gashaving a low degree of capability of absorbing the illuminating light.3. The optical device as claimed in claim 2 , wherein the illuminatinglight has a wavelength of 350 nm or less.
 4. The optical device asclaimed in claim 2 , wherein: upon mounting the optical device on alight passage housing of an illumination optical system disposed in theexposure apparatus, the protective filter is detached while purging thespace with the gas; and the light passage housing is then filled withthe gas.
 5. The optical device as claimed in claim 2 , wherein: uponmounting the optical device on a light passage housing of anillumination optical system of the exposure apparatus, the protectivefilter is detached while purging the space with the gas; anotherprotective filter pre-cleaned is mounted at both ends in the axialdirection of the barrel; and the light passage housing is then filledwith the gas.
 6. The optical device as claimed in claim 2 , wherein: theexposure apparatus is further provided with a stage system to transferthe mask relatively to the illuminating light and to transfer thesubstrate relatively to a projection optical system of the exposureapparatus.
 7. The optical device as claimed in claim 2 , furthercomprising: an illuminating light source for the illuminating lightdisposed separately from the projection exposure apparatus; and a lightsending system having at least one optical element to lead theilluminating light leaving from the illuminating light source to anillumination optical system disposed in the projection exposureapparatus and to adjust a position relationship between an optical axisof the illumination optical system and the illuminating light; whereinthe light sending system is disposed in a barrel which is filled with agas having a lower capability of absorbing the illuminating light.
 8. Anoptical device, comprising: a supply passage which supplies an inert gasinto a barrel with plural optical elements disposed therein; a supplyinlet connected to the supply passage; an exhaust outlet whichdischarges the inert gas in the barrel; and a removing member whichremoves a contaminating material, and which is disposed on an inner wallof the supply passage.
 9. The optical device as claimed in claim 8 ,wherein: the optical device is installed in an apparatus for irradiatinga mask with an illuminating light and exposing a substrate to theilluminating light through the mask; and the inert gas is a gas having alower capability of absorbing the illuminating light.
 10. The opticaldevice as claimed in claim 9 , wherein: the illuminating light has awavelength of 350 nm or less.
 11. The optical device as claimed in claim9 or 10 , wherein: the exposure apparatus further comprises anillumination optical system for irradiating the mask with theilluminating light and a projection optical system for projecting theilluminating light leaving from the mask onto the substrate; and theoptical device is installed at least at a portion of the illuminationoptical system and the projection optical system.
 12. The optical deviceas claimed in claim 11 , wherein: the exposure apparatus is furtherprovided with a stage system to transfer the mask relatively to theilluminating light and to transfer the substrate relatively to aprojection optical system of the exposure apparatus, in synchronizationwith the transfer of the mask.
 13. The optical device as claimed inclaim 11 , wherein: the exposure apparatus further comprises a lightsending system interposed between a light source which emits theilluminating light and the illumination optical system; and the lightsending system is disposed in a housing which is filled with a gashaving a lower capability of absorbing the illuminating light.
 14. Theoptical device as claimed in claim 13 , wherein: the light source isdisposed separately from the exposure apparatus; and the light sendingsystem has an optical element in order to adjust a position relationshipbetween an optical axis of the illumination optical system and theilluminating light leaving from the light source.
 15. The optical deviceas claimed in any one of claims 8 to 10 , further comprising: a movablemember disposed in the supply passage; wherein the removing membercomprises an adsorbing member or a filter.
 16. An optical deviceinstalled in an exposure apparatus to transfer a pattern on a mask ontoa substrate, wherein: the optical device is provided with a removingmember to remove a contaminating material on an inner surface of abarrel with plural optical elements disposed therein; and the opticaldevice is disposed between a light source of an illuminating beam andthe substrate.
 17. The optical device as claimed in claim 16 , wherein:the exposure apparatus comprises a projection optical system to projectan image of the pattern onto the substrate.
 18. An optical device foruse with an exposure apparatus to irradiate a mask with an illuminatinglight and to transfer a pattern on the mask onto a substrate, wherein:the optical device has plural chambers formed between plural opticalelements disposed in a barrel, each chamber being provided with a gassupply inlet and a gas discharge outlet for a gas having a lowercapability of absorbing the illuminating light; and the gas supply inletand the gas discharge outlet being each provided with an opening-closingvalve.
 19. The optical device as claimed in claim 18 , wherein: theexposure apparatus has a projection optical system interposed betweenthe mask and the substrate in order to form an image of the pattern onthe substrate.
 20. The optical device as claimed in claim 18 , wherein:the plural chambers formed between plural optical elements disposed inthe barrel are divided into at least two groups, each group having apredetermined number of chambers; each group being provided with a gassupply inlet and a gas discharge outlet; and the gas supply inlet andthe gas discharge outlet being each provided with an opening-closingvalve.
 21. A method for cleaning an optical device for use with anexposure apparatus for irradiating a mask with an illuminating light andtransferring a pattern on the mask onto a substrate, wherein the opticaldevice has plural chambers formed between plural optical elementsdisposed in a barrel, each chamber being provided with a gas supplyinlet and a gas discharge outlet for a gas having a lower capability ofabsorbing the illuminating light; and the gas supply inlet and the gasdischarge outlet being each provided with an opening-closing valve; saidmethod is characterized by the steps of: filling the barrel with the gasto a predetermined level of pressure in a state in which theopening-closing valve for the gas supply inlet is opened while theopening-closing valve for the gas discharge outlet is closed; allowing acontaminating material attached to a surface of each of the opticalelements to become suspended or afloat by irradiation with theilluminating light in a state in which the opening-closing valves of thegas supply inlet and the gas discharge outlet are closed; flowing thegas outside and inside the barrel by opening the opening-closing valveof the gas supply inlet and the opening-closing valve of the gasdischarge outlet; and closing the opening-closing valves of the gassupply inlet and the gas discharge outlet.
 22. The cleaning method asclaimed in claim 21 , wherein: the gas flows in each of the pluralchambers, prior to closing the opening-closing valve of the gasdischarge outlet, in a state in which the opening-closing valve of thegas supply inlet and the opening-closing valve of the gas dischargeoutlet are both opened.
 23. The cleaning method as claimed in claim 21 ,wherein: the optical device is configured such that the plural chambersare divided into at least two groups, each group having a predeterminednumber of chambers; each group being provided with a gas supply inletand a gas discharge outlet; and the gas supply inlet and the gasdischarge outlet being each provided with the opening-closing valve. 24.A projection exposure apparatus that forms a pattern on a mask onto asubstrate, comprising: an optical device having plural chambers formedbetween plural optical elements disposed in a barrel, each chamber beingprovided with a gas supply inlet and a gas discharge outlet for a gashaving a lower capability for absorbing a illuminating light, and thegas supply inlet and the gas discharge outlet being each provided withan opening-closing valve; wherein: the optical device is cleaned by acleaning method characterized by the steps of: filling the barrel withthe gas to a predetermined level of pressure in a state in which theopening-closing valve for the gas supply inlet is opened while theopening-closing valve for the gas discharge outlet is closed; allowing acontaminating material attached to a surface of each of the opticalelements to become suspended or afloat by irradiation with theilluminating light in a state in which the opening-closing valves of thegas supply inlet and the gas discharge outlet are closed; flowing thegas outside and inside the barrel by opening the opening-closing valveof the gas supply inlet and the opening-closing valve of the gasdischarge outlet; and closing the opening-closing valves of the gassupply inlet and the gas discharge outlet.
 25. The projection exposureapparatus as claimed in claim 24 , wherein: the optical device is usedas the projection optical system disposed on a path of the illuminatinglight in order to transfer the pattern on a mask onto the substrate.and/or an illumination optical system disposed on a path of theilluminating light in order to irradiate the mask with the illuminatinglight.
 26. The projection exposure apparatus as claimed in claim 24 ,further comprising: a stage system connected to the mask and thesubstrate to transfer the mask relatively to the illuminating light andto transfer the substrate relatively to the illuminating light leavingfrom the projection optical system, in synchronization with the transferof the mask.
 27. The projection exposure apparatus as claimed in claim24 , further comprising: a light source system disposed between thelight source and an illumination optical system which irradiates themask with the illuminating light, the light source system being disposedin a housing having a lower capability of absorbing the illuminatinglight.
 28. The projection exposure apparatus as claimed in claim 27 ,wherein: the light source is disposed separately from the projectionoptical system; and the light source system has an optical element inorder to adjust a position relationship between an optical axis of theillumination optical system and the illuminating light leaving from thelight source.
 29. The projection exposure apparatus as claimed in claim24 , wherein: the optical device is configured such that the pluralchambers are divided into at least two groups, each group having apredetermined number of chambers and being provided with a gas supplyinlet and a gas discharge outlet for the gas, and the gas supply inletand the gas discharge outlet being each provided with an opening-closingvalve.
 30. An exposure apparatus which transfers a pattern of a maskonto a substrate, comprising: an optical system interposed between alight source and the substrate; and an optical unit having a protectivefilter disposed at least at an end of a barrel holding an opticalelement and having the barrel filled with a gas having a lowercapability of absorbing the illuminating beam, the optical unit beingdisposed in the optical system.
 31. The exposure apparatus as claimed inclaim 30 , wherein: the optical system includes an illumination opticalsystem disposed on a path of illuminating beam in order to irradiate themask with the illuminating light; and the optical unit is disposed inthe illumination optical system.
 32. The exposure apparatus as claimedin claim 30 , wherein the protective filter is detached from the barrelor replaced with another protective filter upon mounting the opticalunit on the optical system.
 33. The exposure apparatus as claimed inclaim 30 , further comprising: a gas supply device connected to theoptical system to supply a gas having a lower capability of absorbingthe illuminating light to the optical system; wherein the gas supplydevice is operated after the illuminating beam has been irradiated in astate in which the optical system is filled with the gas.
 34. Theexposure apparatus as claimed in claim 33 , further comprising: anexhaust device connected to the optical system to exhaust a gas in theoptical system; wherein the exhaust device is operated before theoptical system is filled or supplied with the gas.
 35. An exposureapparatus which transfers a pattern of a mask onto a substrate,comprising: an optical system interposed between a light source of anilluminating beam and the substrate: a gas supply device which suppliesa gas having a lower capability of absorbing the illuminating beam to atleast a portion of the optical system; and an exhaust device whichexhausts the gas from the at least the portion of the optical systemprior to a supply of the gas.
 36. The exposure apparatus as claimed inclaim 35 , wherein: the optical system comprises an illumination opticalsystem which irradiates the mask with the illuminating beam, a lightsending system interposed between the light source and the illuminationoptical system, and a projection optical system which projects theilluminating beam leaving from the mask onto the substrate.
 37. Theexposure apparatus as claimed in claim 35 , wherein: the exhaust deviceand the gas supply device are operated one after another aftersubjecting the optical system to light cleaning by irradiation with theilluminating beam.
 38. The exposure apparatus as claimed in claim 30 or35 , wherein the illuminating beam has a wavelength ranging from 100 to200 nm.
 39. The exposure apparatus as claimed in claim 38 , wherein: theilluminating beam is ArF excimer laser or F₂ laser; and the gas isnitrogen or helium.
 40. A method for manufacturing an apparatus whichexposes a substrate to an illuminating beam through a mask, comprising:filling a barrel with an optical element disposed therein with a gashaving a lower capability of absorbing the illuminating beam, the barrelbeing provided with a protective filter at least at an end thereof; andinterposing the barrel between a light source of the illuminating beamand the substrate.
 41. The method for manufacturing the exposureapparatus as claimed in claim 40 , wherein: the protective filter isdetached or replaced with another protective filter after the barrel hasbeen disposed.
 42. A method for manufacturing an apparatus which exposesa substrate to an illuminating beam through a mask, said method ischaracterized by the steps of: irradiating at least a portion of anoptical system which leads the illuminating beam to the substrate with acleaning light; and replacing the gas in the optical system with a gashaving a lower capability of absorbing the illuminating beam.
 43. Themethod for manufacturing the exposure apparatus as claimed in claim 42 ,wherein: the gas in the optical system is exhausted therefrom before agas having a lower capability of absorbing the illuminating beam issupplied to the optical system.
 44. The method for manufacturing theexposure apparatus as claimed in claim 42 , wherein: the gas having alower capability of absorbing the illuminating beam is supplied to theoptical system before irradiation with the cleaning light.
 45. Themethod for manufacturing the exposure apparatus as claimed in claim 42 ,wherein: the cleaning light comprises the illuminating beam; and theoptical system comprises an illumination optical system disposed on apath of the illuminating beam in order to irradiate the mask with theilluminating beam, and a projection optical system disposed on a path ofthe illuminating beam in order to project the illuminating beam leavingfrom the mask onto the substrate.
 46. An optical device, comprising: abarrel with plural optical elements disposed therein; a protectivefilter disposed apart in a predetermined distance with respect to anoptical element out of the plural optical elements, which is disposed atleast at one end side in the axial direction of the barrel; and theprotective filter is detachably mounted on the barrel.
 47. The opticaldevice as claimed in claim 46 , wherein: the protective filter isdetachably mounted each on the both end portions in the axial directionof the barrel.
 48. The optical device as claimed in claim 47 , wherein:an inert gas is filled in a chamber interposed between the pluraloptical elements and in a space interposed between the optical elementsdisposed on the both end sides and the plural protective filter.
 49. Theoptical device as claimed in claim 48 , wherein: the optical device isinstalled in an apparatus that forms a pattern on a mask onto asubstrate; and the inert gas is a gas having a lower capability ofabsorbing the illuminating light.
 50. A method of storing an opticaldevice with plural optical elements disposed; wherein: the opticaldevice has a barrel with plural optical elements disposed therein; themethod of storing is characterized by the steps of: irradiating asurface of each of the optical elements with a light for removing acontaminating material attached on the surface of each of the opticalelements; filling the barrel with an inert gas to a predetermined levelof pressure after the contaminating material removed from the surface ofeach of the optical elements has been discharged from the barrel; andstoring the optical device in a state in which the barrel is filled withthe inert gas.
 51. The method of storing as claimed in claim 50 ,wherein: the optical device is provided with a gas supply inletconnected to the barrel to supply the inert gas into the barrel and agas discharge outlet connected to the barrel to discharge the gas in thebarrel, the gas supply inlet and the gas discharge outlet being eachprovided with an opening-closing valve; the storing method ischaracterized by the steps of: filling the barrel with the inert gas toa predetermined level of pressure by opening the opening-closing valvefor the gas supply inlet and closing the opening-closing valve of thegas discharge outlet, prior to irradiating the surface of the opticalelement with the light; floating the contaminating material byirradiating the surface of the optical element with the light afterclosing the opening-closing valve of the gas supply inlet in a state inwhich the pressure in the barrel has reached its predetermined level ofpressure; flowing the inert gas inside and outside the barrel by openingthe opening-closing valves of the gas supply inlet and the gas dischargeoutlet; and closing the opening-closing valves of the gas supply inletand the gas discharge outlet after the inert gas has been allowed toflow inside and outside the barrel.
 52. The method of storing as claimedin claim 50 , wherein: the optical device is provided with a gas supplyinlet connected to the barrel to supply the inert gas into the barreland a gas discharge outlet connected to the barrel to discharge the gasin the barrel, the gas supply inlet and the gas discharge outlet beingeach provided with an opening-closing valve; the storing method ischaracterized by the steps of: discharging the contaminating material,together with the inert gas, from the barrel through the gas dischargeoutlet; filling the barrel with the inert gas to a predetermined levelof pressure by opening the opening-closing valve for the gas supplyinlet and closing the opening-closing valve of the gas discharge outlet,after discharging the contaminating material; and closing theopening-closing valve of the gas supply inlet after the inert gas hasbeen filled.
 53. The method of storing as claimed in claim 52 , whereinthe surface of the optical element is irradiated with the light in astate in which the opening-closing valves of the gas supply inlet andthe gas discharge outlet are opened.
 54. The method of storing asclaimed in claim 50 , wherein the light has a wavelength of 350 nm orless.
 55. The method of storing as claimed in claim 50 , wherein: theoptical device has each of plural chambers provided with the gas supplyinlet and the gas discharge outlet, each chamber being formed betweenplural optical elements disposed in the barrel.
 56. The method ofstoring as claimed in claim 50 , wherein: the optical device isinstalled in an apparatus that forms a pattern on a mask onto asubstrate.
 57. The method of storing as claimed in claim 56 , whereinthe apparatus is an exposure apparatus.
 58. The method of storing asclaimed in claim 50 , wherein the optical device comprises an alignmentoptical device which detects a position of an alignment mark formed on amask or a substrate.
 59. The method of storing as claimed in claim 50 ,wherein the optical device comprises an measurement device whichmeasures an optical characteristic of a projection optical device whichtransfers a pattern of a mask onto a substrate.
 60. A method ofmanufacturing an exposure apparatus which exposes a substrate with anilluminating beam through a mask, wherein: the exposure apparatus has alight passage housing to cover a light passage of the illuminating beamand an opening-closing valve on the housing side connected to a pipe forsupplying an inert gas; and an optical device to be mounted on the lightpassage housing comprises a barrel having plural optical elementsdisposed therein and being filled with an inert gas, a gas supply inletconnected to the barrel to supply the inert gas to the inside of thebarrel, and a gas discharge outlet connected to the barrel to dischargethe inert gas inside the barrel, the gas supply inlet and the gasdischarge outlet being provided each with an opening-closing valve; saidmanufacturing method is characterized by the steps of: installing theoptical device in the light passage housing by opening the light passagehousing; connecting the pipe to the gas supply inlet; opening theopening-closing valve for the gas supply inlet and the opening-closingvalve for the gas discharge outlet; and closing the light passagehousing.
 61. The method of manufacturing the exposure apparatus asclaimed in claim 60 , wherein: the optical device is further providedwith a protective filter disposed apart in a predetermined distance withrespect to an optical element out of the plural optical elements, whichis disposed on an end side in the axial direction of the barrel; saidmanufacturing method is characterized by the steps of: supplying theinert gas to the inside of the barrel by opening the opening-closingvalve on the side of the housing side and the opening-closing valve ofthe gas supply inlet in a state in which the opening-closing valve ofthe gas discharge outlet is closed, after the gas supply inlet has beenconnected to the pipe for supplying the inert gas; detaching theprotective filter in a state in which the inert gas has been supplied;and opening the opening-closing valve of the gas discharge outlet. 62.The method of manufacturing the exposure apparatus as claimed in claim61 , wherein: a new protective filter is mounted after the protectivefilter has been detached, in a state in which the inert gas is supplied;and the opening-closing valve of the gas discharge outlet is openedafter mounting the new protective filter.
 63. The method ofmanufacturing the exposure apparatus as claimed in claim 62 , wherein:the exposure apparatus has a gas discharge outlet on a main body side todischarge a gas in the light passage housing, the gas discharge outletbeing provided with an opening-closing valve; said manufacturing methodis characterized by the steps of: discharging the gas in the lightpassage housing by opening the opening-closing valve of the gasdischarge outlet on the main body side, after the optical device hasbeen disposed in the light passage housing.
 64. An optical devicecomprising: a gas supply passage which supplies an inert gas into abarrel with plural optical elements disposed therein; a gas supply inletconnected to the gas supply passage; an opening-closing valve whichcontrols a flow rate of the inert gas, which is disposed in the gassupply inlet; and a filter which removes a contaminating materialcontained in the inert gas, which is disposed in the gas supply passagebetween the gas supply inlet and the opening-closing valve.
 65. Theoptical device as claimed in claim 64 , wherein: a removing member whichremoves the contaminating material is disposed on an inner wall of thebarrel.
 66. The optical device as claimed in claim 65 , wherein: aremoving member which removes a contaminating material is disposed on aninner wall of the barrel.
 67. The optical device as claimed in claim 66, wherein: the optical device is installed in an apparatus forirradiating a mask with an illuminating light and exposing a substrateto the illuminating light through the mask; and the inert gas comprisesa gas having a lower capability of absorbing the illuminating light. 68.An exposure apparatus which transfers a pattern on a mask onto asubstrate, comprising: a barrel with plural optical elements disposedtherein; a gas supply passage which supplies an inert gas into thebarrel; a gas supply inlet connected to the gas supply passage; anopening-closing valve which controls a flow rate of the inert gas, whichis disposed on the gas supply passage; and a filter which removes acontaminating material contained in the inert gas, which is disposed onthe gas supply passage locating between the gas supply inlet and theopening-closing valve.
 69. The exposure apparatus as claimed in claim 68, wherein: the barrel is provided at least in an illumination opticalsystem disposed on a path of the illuminating light to irradiate themask with an illuminating light or-a projection optical system disposedon a path of the illuminating light to project the illuminating lightleaving from the mask onto the substrate.
 70. A method for cleaning anoptical device for use with an exposure apparatus which transfers apattern on a mask onto a substrate by irradiating the mask with anilluminating light, wherein: the optical device has plural chambers,each of which is provided with a gas supply inlet connected to a barrelto supply a gas having a lower capability of absorbing the illuminatinglight and a gas discharge outlet connected to the barrel to dischargethe gas, each chamber being formed between plural optical elementsdisposed in the barrel therein, the gas supply inlet and the gasdischarge outlet being each provided with an opening-closing valve; thecleaning method is characterized by the steps of: allowing acontaminating material attached to a surface of each of the opticalelements by irradiating the optical elements with the illuminatinglight; and flowing the gas outside and inside the barrel by opening theopening-closing valves of the gas supply inlet and the gas dischargeoutlet.
 71. A projection exposure apparatus which irradiates a mask withan illuminating light and which transfers a pattern on the mask onto asubstrate through a projection optical system; comprising: an opticaldevice having plural chambers, each of which is provided with a gassupply inlet connected to a barrel to supply a gas having a lowercapability of absorbing the illuminating light and a gas dischargeoutlet connected to the barrel to discharge the gas, each chamber beingformed between plural optical elements disposed in the barrel therein,the gas supply inlet and the gas discharge outlet being each providedwith an opening-closing valve; wherein the optical device is subjectedto a cleaning method characterized by the steps of: allowing acontaminating material attached to a surface of each of the opticalelements by irradiating the optical elements with the illuminatinglight; and flowing the gas outside and inside the barrel by opening theopening-closing valves of the gas supply inlet and the gas dischargeoutlet.
 72. An exposing method for irradiating a mask with anilluminating light and transferring a pattern on the mask onto asubstrate through a projection optical system, said method ischaracterized by the steps of: supplying a gas having a lower capabilityof absorbing the illuminating light to each of plural chambers eachbeing formed between plural optical elements disposed in a barrel;floating a contaminating material attached to a surface of each of theplural optical elements by irradiating the plural optical elements witha light for removing the contaminating material in a state in which thegas is supplied; flowing the gas outside and inside the barrel for eachof the plural chambers; filling the plural chambers with the gas afterflowing the gas; and transferring the pattern onto the substrate in astate in which the plural chambers are filled with the gas.
 73. Theexposing method as claimed in claim 72 , wherein: the plural chambersare filled with the gas, after flowing the gas; and the pattern istransferred onto the substrate in a state in which the plural chambersare filled with the gas.
 74. The exposing method as claimed in claim 72, wherein: the pattern is transferred onto the substrate whilecontinuing the supply of the gas to the plural chambers, after flowingthe gas.
 75. The exposing method as claimed in claim 72 , wherein thelight for removing the contaminating material comprises the illuminatinglight.